Railway signaling system



G w. BAUGHMA-N 2,243,726 RAILWAY SIGNALING SYSTEM May 27, I941.

Filed March 8, 1940 IN NTOR "I 9&1226272.

Geo/rye BY r Patented May 27, 1941 res RARWAY SIGNALING SYSTEMApplication March 8, 1940, SerialNo. 322,974

11 Claims. (01. 246-130) My invention relates to railway traificcontrolling apparatus of the type employing coded current in the trackcircuits thereof, and more particularly to the provision in a system ofthis character of improved track circuit detection means for the controlof highway crossing signals or other apparatus.

Where a track section includes an intersection with a highway it iscustomary to divide the track section into subsections to facilitatecontrol of the crossing signals which protect the intersection. Onentrance of a train into the rearward or approach subsection operationof the crossing signals is initiated, while when the train vacates therearward subsection it is desired to discontinue operation of thecrossing signals without conditioning the signals governing movement oftrains in the track section to display a proceed indication.

It has heretofore been proposed to provide in a system of this kindmeans operative when a train enters the forward or clearing sussectionto supply to the track rails of the rearward subsection steady uncodedenergy, and to provide means associated with the rearward subsection andoperative on the supply of steady energy thereto to discontinueoperation of the crossing signals.

If steady energy is supplied to a track circuit in which coded energy isnormally employed, the

advantage of improved shunting sensitivity which results from the use ofcoded current in the track circuit is lost as long as steady energy issupplied to the track circuit. Accordingly a following train enteringthe track section at a time when steady energy is supplied thereto mightnot effectively shunt the track relay for the section with the resultthat operation of the crossing signals would not be started and users ofthe highway would not be warned of the approach of the train.

It is an object of my invention to provide an improved railway signalingsystem of the type employing coded current in the track circuits thereofto control the signals governing movement of trains through the trackstretch, the system also employing coded current in the track circuitsfor detection purposes to thereby provide the same degree of shuntingsensitivity at such times as is normally obtained in the track circuits.

A further object of my invention is to provide, 3

in a railway signaling system of the type employing coded current in thetrack circuits thereof to control the signals governing movement oftrains through the track stretch, means to supply coded energy of adistinctive character to a track ciri cuit to detect occupancy of thesection Without affecting the signals governing traflic in the trackstretch.

Another object of my invention is to provide an improved railwaysignaling system having a track section having a track circuit includingmeans responsive to coded current of one relative polarity forcontrolling the signals which govern movementof trains through the tracksection, and having means responsive to coded current of the otherrelative. polarity for detecting occupancy of the track section tothereby enable coded current to be employed to detect occupancy of thetrack section without interfering with the means controlling the signalsgoverning trafiic in the track section.

A further object of my invention is to provide an improved signalingsystem of the type de-.

scribed and adapted for use in track stretches r where coded alternatingcurrent is supplied to the track rails of the track sections to actuatevehicle carried signal apparatus, the system being arranged so that whencoded direct current of the polarity employed for detection purposes issupplied .to a track section coded alternating current will not besupplied thereto to thereby insure that at such times the vehiclecarried signaling apparatus will be conditioned to provide its inostrestrictive indication.

Another object of my invention is to provide an improved railwaysignaling system.

I shall describe one form of apparatus embodying my invention, and shallthen point out the novel features thereof in claims.

In the drawing the single figure is a diagram of a stretch of railwaytrack equipped with coded signaling apparatus embodying my invention.

Referring to the drawing, there is shown therein a stretch of railwaytrack having track rails l and 2 over which traific normally moves inthe direction indicated by the arrow, that is, from left to right. Therails of the track stretch are divided by insulated joints 3 into tracksections for signaling purposes. One of these sections includes anintersection with a highway and the rails of this section have insulatedjoints 3 therein to divide the section into subsections to facilitatecontrol of the interlocking relay XR, which controls the crossingsignals XS which protect the highway intersection. The two subsectionsare designated Al H and Bi 1T, while portions of two track sections areshown and are designated MT and I2T.

Each of the principal track sections has adjacent the entrance endthereof a wayside signal,

designated S with an appropriate prefix, for governing movement oftrains in the track section. As shown the signals are of the familiarcolor light type, each having a green or clear lamp G, a yellow orcaution lamp Y, and a red or stop lamp R. The invention, however, is notlimited to a system employing this type of wayside signals, and anysuitable signals may be employed. Furthermore, the invention is notlimited to a signaling system employing wayside signals, but is equallyapplicable to a system which has cab signals only.

The rails of each of the track sections form a part of a track circuitto which direct current coded or periodically interrupted at either of aplurality of different frequencies is supplied at a point adjacent theexit end of the track section to control the wayside signals, whilecoded alternating current is also supplied to the track circuits tooperate cab signaling apparatus carried by locomotives operating throughthe track stretch.

Each of the-track sections has adjacent the entrance end thereof a codefollowing track relay TR having a winding receiving energy from therails of the associated track section. The track relays are of a typewhich are responsive to direct current of one relative polarity only,while current of opposite relative polarities is employed in the trackcircuits of adjoining track sections to prevent improper operation ofthe track relay of one of the sections in the event the insulated jointsseparating the rails of the sections become defective.

The subsection BI IT is provided with an auxiliary code following trackrelay BI I TRA having its winding connected in series with that of theprincipal track relay BI ITR. The relays BI ITR rand BIITRA are arrangedso that one relay responds to current of one polarity only and so thatthe other responds to current of the other polarity only.

The track relays IZTR, and BI I TR each have associated therewithdecoding means selectively responsive to code following operation of therelay to control the associated signal, and to also control the supplyof coded direct and alternating current to the rails of the adjoiningtrack section in the rear. As shown the decoding means associated witheach of these track relays comprises a decoding transformer DT,auxiliary relays H and J, a code transmitter CT, a track transformer TT,and a track battery TB.

The primary windings of the track transformers T are, supplied withalternating current from a suitable source, the terminals of which aredesignated BX and CX, while each of the track relays has associatedtherewith a source of direct current the terminals of which aredesignated B and C in the drawing.

The decoding means associated with the track relays IZTR and BIITR isnot a part of this invention and any suitable means of this type may beemployed.

The track relays AI ITR and BI ITR each have associated therewitha frontcontact repeater relay FSA and a back contact repeater relay BSA. Thetrack relay AI ITR also has associated therewith a track transformer BIITT, a code transmitter AI ICT, and a track battery BI ITB.

As shown the code transmitters I ICT and I ZCT have continuouslyoperated contacts I88 and I5 which provide track circuit current of twocode frequencies, namely, current of 180 interruptions per minute overthe periodically closed contact I83, and current of '75 interruptionsper minute over the periodically closed contact I5.

The code transmitter AIICT has one circuit making and breaking contact28. While the coded direct current which is supplied to the rails ofsection BI IT for detection purposes may be of any desired frequency, itis preferred to employ a code frequency, such as 20 impulses per minute,which is substantially lower than the code frequencies employed in thecontrol of the signals.

The equipment is shown in the condition which it assumes when the trackstretch is vacant. At this time coded direct current of the codefrequency is supplied to the rails of section I2T by the means, notshown, associated with the adjacent section in advance. This energy isof the polarity which is effective to produce code following operationof the track relay IZTR.

As a result of movement of contact 22 of the track relay IZTR, betweenits picked-up and released positions, the two end portions of theprimary winding 2I of the decoding transformer I2DT are alternatelyenergized with the result that energy is induced in the secondarywindings 23 and 24 of the transformer. The contact 25 of the relay IZTRrectifies the current supplied from the secondary winding 23 of thetransformer IZDT to the Winding of the relay I2H and the contacts of therelay IZH are maintained picked up.

As the relay IZTR is responding to energy of the 180 code frequency, thefrequency of the current induced in the secondary winding 24 is suchthat suflicient energy is supplied through the resonant rectifier unitIZRU to maintain the contact of the relay IZJ picked up.

As contact 21 of relay IZH and contact 28 of relay IZJ are picked up,the circuit of the green lamp G of signal I2S is established and thislamp is lighted. As contact 39 of relay I2H is picked up, the circuit ofthe I88 contact of the code transmitter I2CT is established and thecircuit of the track battery IZTB and of the secondary winding 32 of thetrack transformer IZTT is intermittently established so as to supplycoded alternating and direct current of the 180 code frequency to therails of the clearing section AI IT.

The coded alternating current supplied to the rails of section AIITserves to control vehicle carried signal apparatus on trains traversingthe track section, while the coded direct current effects operation ofthe track relay AI ITR.

On the supply of coded direct current to the track relay AIITR thecontacts 35 and 36 are picked up and released. During the picked upperiods of the contact 35 energy is supplied to the winding of relayAIIFSA, while during the released periods of contact 35 energy issupplied to the winding of relay AI IBSA over a circuit which includesfront contact 38 of relay AI IFSA. A resistor 48 is connected across theterminals of the winding of relay AI IFSA to render the relay contactsslow to release, while contact 38 when picked up establishes a circuitto connect a resistor 4| across the terminals of the winding of therelay AI IBSA to render the contacts of this relay slow to release.Accordingly, as the track relay A] I TB. is responding to coded energy,the relays AI IFSA and AIIBSA are both energized and their contacts arepicked up, while the contacts of these relays are slow enough inreleasing to remain picked up during the intervals between the supply ofimpulses of energy to the relay windings.

As the contacts 43 and 44 of the relays AI IBSA are picked up, a circuitis established to supply direct current energy of normal relativepolarity from the track battery BI ITB to the rails of the approachsection BI IT during the released periods of the track relay contact 36.This circuit is traced from track rail 2 of section BI IT through wire55 and front contact 44 of relay AIIBSA to one terminal of the trackbattery BI ITB, and from the other terminal of the battery through frontcontact 43 of relay Al IBSA, back contact 36 of track relay Al ITR, andwire 46 to track rail I of section BI IT.

The circuit for supplying direct current to the rails of the approachsection BI IT is interrupted during the picked-up periods of the trackrelay contact 35. Accordingly energy of the same code frequency issupplied to the rails of section BI IT as is supplied to the track relayAI ITR.

During the picked up periods of the track relay contact 36 a circuit isestablished for supplying energy from the secondary winding 32 of thetrack transformer BIITT to the rails of section BIIT. This circuit istraced from rail 2 of section BI IT through wire 45 to one terminal ofthe transformer secondary winding 32, and from the other terminal of thewinding 32 through front contact 36 of the track relay AI ITR and wire46 to rail I of section BI IT.

The circuit for supplying alternating current to the rails of section BEIT is interrupted during the released periods of the track relay contact36 with the result that the alternating current supplied to the rails ofsection BIIT is coded at the same code frequency as the direct currentsupplied to the track relay AI ITR.

From the foregoing it will be seen that when the track relay AIITR isresponding to coded energy, impulses of direct current are supplied tothe rails of section BI IT during the released periods of the trackrelay contacts, and that during the picked-up periods of the track relaycontacts impulses of alternating current are supplied to the rails ofsection BI IT.

In addition it will be seen that during the picked-up periods of thetrack relay contacts a shunt circuit is established between the trackrails I and 2 of section BE IT through the secondary winding 32 of tracktransformer BI ITT.

This circuit is of relatively low resistance and provides means todissipate any charge built up between the track rails I and 2 by thesupply of impulses of direct current thereto. As the track rails areshunted during the intervals between the supply of impulses of directcurrent energy thereto, the accumulation of a charge between the trackrails which might interfere with operation of the track relays isprevented.

At this time as contact 48 of relay AI IBSA is picked up, the circuit ofthe winding 49 of interlocking relay XR is established and this windingis energized.

As the track stretch is assumed to be vacant, coded direct currentsupplied to the rails of section BIIT feeds to the track relays BI ITRand BIITRA and flows through the windings of these relays in series. Asstated above, the track relays Bi iTR and Bi ITRA are arranged so thatthey respond to current of opposite relative polarities. are arranged sothat only the relay BI ITR. will The relays Bi I'I'R. and BI ITRArespond to energy of the polarity which is supplied thereto when thecontacts of the relay AI I BSA are picked up. Accordingly at this timeth relay BI ITR responds to coded direct ourrent, while the contact ofthe relay BI ITRA remains in its released position.

As the contact 50 of relay BI ITRA remains As a result of code followingoperation of the track relay BIITR, energy is supplied through thedecoding transformer BIIDT to the relays BI IE and BI IJ in the mannerdescribed in detail in connection with section IZT.

As the contacts of relays BI Ii-I and BI IJ are picked up, the circuitof the green or clear lamp G of signal IIS is established. In addition,as contact 3d of relay BIIH is picked up, the circuit for supplyingcoded alternating and direct current of the code frequency to the railsof section IBT is established.

The relay BI iH has another contact 5| which when picked up establishesa circuit to supply energy to the winding 53 of interlocking relay 253.As both windings of the relay XR. are energized, this relay maintainsthe crossing signals XS inactive.

Operation. of equipment on passage of a train in normal direction oftmfiic When a train moving in the normal direction of tralfic enters theapproach section BI IT, the track relay BI ITR is shunted and no longerresponds to coded energy. At this time the cab signal equipment carriedby the locomotive responds to the alternating current of 180 codefrequency supplied by the equipment associated with relay AIITR andprovides the engineer with a clear signal.

As the relay BI ITR is shunted, energy is no longer supplied through thedecoding transformer Bl iDT to the relays BI IE and BI IJ and thecontacts of these relays become released.

As a result of release of contact 21 of relay iII-I, the circuit of thegreen lamp G of signal IIS is interrupted, and the circuit of the red orstop lamp R is established. As a result of release of contact 38 ofrelay BI IH, the circuit for supplying energy of the 180 code frequencyto the rails of section I ET is interrupted and the circuit forsupplying energy of the 75 code frequency is established.

In addition, as a result of the release of the contacts of relay BIIH,contact 5i interrupts the circuit for supplying energy to the winding 53of interlocking relay XE. Accordingly, the armature controlled by thiswinding becomes released and eifects operation of the crossing signalsXS to warn users of the highway of the approach of a train.

When the train advances far enough in the track stretch to enter theclearing section AI IT, the track relay AI iTR. is shunted and itscontacts remain released. As contact 35 of relay AIiTR does not engageits front contact, en

of the contacts 43.

is established for supplying energy of the opposite or reverse relativepolarity from the battery BI ITBto the rails of section BI IT. Thiscircuit includes contact 20 of the code transmitter AI ICT and is tracedfrom.- rail 2 of section BI IT through wire 45 and back contact 43 ofrelay AI IBSA to one terminal of the battery BI ITB, and from the otherterminal of the battery through back contact 44 of relay AI IBSA, frontcontact 20 of the code transmitter AI'ICT, back contact 55 of relay AIIBSA, and wire $6 to rail I of section BIIT. This circuit is interruptedduring the released periods of contact 20 of the code transmitter AIICT, and the rate of operation of contact 20 is such as to close thecircuit for supplying energy to the rails of section BI IT twenty timesa minute and to provide the same number of intervals of substantiallyequal duration during which energy is not supplied to the rails ofsection BI IT.

During the released periods of contact 213 of the code transmitter AIICT a circuit is established which shunts the rails of the section BIIT. This circuit is traced from track rail I of section BI IT throughWire 45, back contact 55 of relay AIIBSA, back contact 20 of codetransmitter AI ICT, and wire 45 to rail 2 of section BIIT. Since therails of section BII T are shunted during the intervals between thesupply of impulses of current thereto, the accumulation of a chargebetween the track rails at this time is prevented.

As a result of release of the contacts of relay AIIBSA, contact 48interrupts the circuit of winding 49 of interlocking relay XR. However,because of the internal construction of the re lay m, the armaturecontrolled by winding 49 is prevented from moving all of the way to itsreleased position since the armature controlled by winding 53 is alreadyreleased.

As long as any portion of the train remains in the approach section BIIT, the track relays Bl ITR and BI I'IRA continue to be shunted, but assoon as the rear of the train vacates section BI IT, coded directcurrent supplied to the rails of the section feeds to the track relaysBI ITR. and BI ITRA.

The polarity of the direct current impulses supplied at this time issuch that the track relay BIITRA will respond to these impulses, whilethe relay BI I TR will not respond to these impulses and its contactsremain in their released positions.

As the contacts of the relay BI ITR remain in their released positions,the signal I IS continues to display its stop indication, while energyof the 75 code frequency continues to be supplied to the rails ofsection IElT.

On movement of the contact 59 of relay BI ITRA to its picked up positionenergy is supplied to the winding of relay BI IFSA, and the contact ofthis relay becomes picked up so that on movement of contact 58 to itsreleased position energy is supplied to the winding of the relay BIIBSA. The relays BI IFSA and BI IBSA have snubbing resistors associatedtherewith to render the relay contacts slow in releasing, and theserelays and the resistors are selected so that the relay contacts willremain picked up during the intervals between the supply of impulses ofenergy to the relay windings.

As a result of the supply of energy to the winding of relay BI IBSA,contact 55 of the relay becomes picked up and establishes a circuit tosupply energy to the winding 53 of the interlocking relay XR. Thearmature controlled by this winding accordingly becomes picked up andoperation of the crossing signals XS is discontinued, while, because ofthe internal construction of the relay, the armature controlled by thewinding 49 continues to be prevented from moving to its releasedposition.

When the train advances far enough to enter the track section I2T, thetrack relay IZTR is shunted and energy is no longer supplied through thedecoding transformer IZDT to the windings of the relays IZH and IN.Accordingly the contacts of these relays become released and conditionthe signal I 2S to display its red or stop indication, while the energysupplied to the rails of the clearing section AIIT is changed from theto the 75 code frequency.

As long as a portion of the train remains in section AI IT, the trackrelay Al I TB is shunted, but when the rear of the train vacates thesection, coded direct current of the 75 code frequency feeds to thewinding of the track relay AI ITR and produces code following operationof the track relay contacts, and as a result the contacts of the relaysAI IFSA and AI I BSA become picked up.

On picking up of the contacts 43 and 44 of relay AI I BSA, the circuitcontrolled by contact 20 of the code transmitter AI ICT for supplyingenergy of reverse relative polarity to the rails of section BI IT isinterrupted, While the circuit is established for supplying energy ofnormal relative polarity to the rails of section BIIT during thereleased periods of the track relay contact 36.

In addition, as a result of picking up of the contacts of the relay AIIBSA, contact 55 interrupts the circuit controlled by code transmittercontact 20 for shunting the rails of the section BI IT, while contact 48of relay AI IBSA establishes the circuit for supplying energy to thewinding 49 of the interlocking relay XR. On the supply of energy to thiswinding the armature controlled by the winding is picked up and therelay is restored to its normal condition.

On movement of the track relay contact 36 to its picked-up position thecircuit is established for supplying impulses of alternating current tothe rails of section BI IT and for shunting the track rails of thesection, as explained above.

At this time as the track relay AI ITR. is responding to energy of the75 code frequency, the energy supplied to the rails of section BIIT iscoded at this frequency.

On interruption of the supply of impulses of direct current of reverserelative polarity to the rails of section BI IT the track relay BI ITRAceases to respond to coded energy, while on the supply of impulses ofdirect current of the normal relative polarity to the rails of sectionBI IT the track relay BI ITR responds to coded energy and energy issupplied through the decoding transformer BI IDT to the winding of therelay BI IH.

It will be seen that on each movement of the contacts of the track relayBI ITR to their picked-up or released positions there is a, change inenergization of the decoding transformer primary winding, and thatcontact 25 of the relay establishes a circuit to supply an impulse ofenergy from the transformer secondary winding to the winding of relay BIIH.

The relay BI IH and the transformer BIIDT are selected and proportionedso that the contacts of the relay when released will not become pickedup as a result of the supply of one impulse of energy from thetransformer to the relay winding, or on the continued supply of impulsesof energy at the frequency at which they are supplied when the trackrelay is responding to energy of a code frequency substantially lowerthan the 75 code frequency, such as, for example, energy of the 20 codefrequency.

The relay BHH and the transformer Bl IDT are also selected andproportioned so that the relay contacts when released will become pickedup on the supply in rapid succession of a plurality of impulses ofenergy from the decoding transformer, such as are supplied to the relaywinding when the track relay is responding to energy of the '75 codefrequency.

Since at this time the track relay Bl lTR is responding to energy of the'75 code frequency, impulses of energy are supplied to the winding ofrelay Bill-I which are effective to pick up the relay contacts after aplurality of such impulses of energy have been supplied to the relaywinding. As the track relay Bl [TR is responding to energy of relativelyhigh code frequency, and since impulses of energy are supplied to thewinding of the relay Bl EH in both the picked-up and released positionsof the track relay contacts, the plurality of impulses of energynecessary to pick up the contacts of the relay BI [H are supplied to thewinding of the relay BHH Very quickly after initiation of code followingoperation of the track relay Bl ITR.

It will be seen also that on initiation of code following operation ofthe track relay AHTR the supply of energy of reverse relative polarityto the rails of section Bl IT is continued until the contacts of relayAl I BSA become picked up,

and that on picking up of the contacts of relay Al IBSA the supply ofenergy of normal relative polarity to the rails of section Bl IT isinitiated immediately. Accordingly, there is no time delay betweencessation of code following operation of the track relay Bl lTRA andinitiation of code following operation of the relay Bl ITR.

Because of the slow releasing characteristic of the relay BllFSA a shorttime interval must elapse after the track relay BHTRA ceases to followcode before the contacts of the relay BI lFSA become released, while thecontacts of the relay Bl lBSA release soon thereafter.

On release of the contact 56 of relay Bl IBSA the circuit which itcontrols for supplying energy to the winding 53 of the interlockingrelay XR is interrupted. However, as pointed out above, at this time thecontacts of the relay Bl IH become picked up promptly, and the variousparts of the equipment are arranged so that the contact El of relay BllHbecomes picked up to establish the circuit which it controls before thecontact of relay Bl IBSA becomes released. Accordingly on the change inthe supply of energy to the rails of section Bl lT from energy ofreverse relative polarity to energy of normal relative polarity there isno interruption in the supply of energy to the winding 53 of theinterlocking relay XR, and this relay, therefore, maintains the crossingsignals XS inactive.

At this time as the track relay Bl lTR is responding to coded energy ofthe 75 code frequency, the contacts of the relay Bl IH are picked up,but insufficient energy is supplied through the resonant unit Bl IRU tothe winding of the relay Bl U to pick up the contacts of this relay. Asthe contact 28 of relay Bl U is released, and as the contacts of therelay BHH are picked up, the signal l is is conditioned to display itsyellow or caution indication, while contact 30 of relay B! IH interruptsthe circuit for supplying energy of the 75 code frequency to the railsof section I01 and establishes the circuit for supplying energy of codefrequency thereto.

When the train vacates section I2T, energy of the 75 code frequencysupplied to the rails of this section by the means associated with thetrack relay of the adjacent section in advance feeds to the' relay EZTRand the equipment associated with this relay conditions the signal |2Sto display its caution indication, while the energy supplied to therails of section AI IT is changed from 75 to 180 code frequency.

On this change in the frequency of the energy supplied to the rails ofsection AI IT there is an increase in the rate of operation of thecontacts of the track relay Al I'IR, and a corresponding change in thefrequency of the code supplied to the rails of section BIIT. Accordinglythe contacts of relay BII'IR operate at a higher rate and sufficientenergy is supplied through the resonant unit Bl lRU to pick up thecontact of relay Bl lJ withthe result that signal HS displays its clearindication instead of its caution indication.

From the foregoing, it will be seen that the system provided by thisapplicant normally employs coded direct current in the track circuits ofthe various track sections to control the signals governing movement oftrains through the track stretch and to normally maintained the crossingsignals inactive.

It will be seen also that on passage of a train through the trackstretch, that when the train enters the clearing subsection in advanceof the crossing, the supply of coded energy of normal relative polarityto the rails of the approach subsection in the rear of the crossing isout off, while coded energy of reverse relative polarity .is supplied tothe rails of the rearward or approach subsection.

The track circuit apparatus associated with the rearward subsection andcontrolling the signals governing traflic in the track stretch will notrespond to energy of this relative polarity, and, therefore, the waysidesignal controlled by this apparatus continues to display its mostrestrictive indication.

However, the approach subsection in the rear of the intersection hasmeans including an auxiliary track relay which is responsive to thesupply of coded energy of reverse relative polarity, and is operative todiscontinue operation of the highway crossing signals and to thereaftermaintain the crossing signals inactive as long as coded energy ofreverse relative polarity continues to be supplied to the auxiliarytrack relay.

If a second train enters the rearward or approach subsection at a timewhen coded current of reverse relative polarity is being suppliedthereto, the auxiliary track relay will be shunted and the relays BlIFSA and Bi lBSA controlled thereby will become deenergized and contact56 of relay Bl lBSA will interrupt the circuit for supplying energy tothe winding 53 of the interlocking relay XR so that this relay willinitiate operation of the crossing signals XS to warn users of thehighway of the approach of the train.

It will be seen that at this time the shunting sensitivity of the trackcircuit of the rearward subsection is determined by the code followingauxiliary track relay BHTRA with the result that the shuntingsensitivity of the track circuit is the same when energy is supplied tothe track circuit to discontinue operation of a crossing signal as it iswhen energy is supplied to the track circuit to control the signalsgoverning trafiic in the track stretch.

In addition it will be seen that when coded direct current of reverserelative polarity is supplied to the approach section that the supply ofcoded alternating current to the rails of the section is interrupted sothat if a train enters the subsection the cab signal apparatus on thelocomotive Will display its most restrictive indication.

Furthermore, it will be seen that the frequency of the coded currentsupplied to the rails of the subsection in the rear of the crossing forthe purpose of discontinuing operation of a crossing signal is muchlower than the frequency of the code employed for the control of thetraflic governing signals. If for any reason the track relay BIITRshould respond to the energy of this low code frequency, insufiicientenergy would be supplied through the decoding transformer BI IDT to therelay BI II-I to pick up the relay contacts and the signal II S,therefore, would continue to display its stop indication. Similarly, ifa train should enter the rearward subsection at a time when the forwardsubsection is occupied,'the cab signal equipment on the locomotive wouldnot respond to energy of this low code frequency to provide a proceedindication, even if for any reason coded alternating current weresupplied to the rails of the track section.

Operation of equipment on movement of a train through the track stretchin the reverse direction The system provided by this invention isarranged so that the crossing signals and the traffic energy of the 180code frequency and the signals I28 and IIS are conditioned todisplaytheir green or clear indications,

When the train enters the adjacent section in advance of section IZT,the energy supplied to the rails of section I2T is changed from 180 to75 code frequency with the result that signal IZS is conditioned todisplay its yellow or caution indication, while energy of 180 codefrequency continues to be supplied to the rails of section AI IT.

When the train enters section IZT, the track relay IZTR is shunted andthe signal IZS is conditioned to display its red or stop indication,while the energy supplied to the section in the rear is changed from 180to '75 code frequency. The track relay AIITR responds to the lower codefrequency and repeats the supply of ener y of the 75 code frequency tothe rails of section BI IT, while the signal H is conditioned to displayits yellow or caution indication instead of its green or clearindication.

At this time as the track relays AIITR and BI ITR are responding tocoded energy, the circuits are established to supply energy to both ofthe windings of the interlocking relay XR and this relay maintains thecrossing signal XS inactive.

When the train advances into section AIIT, the track relay of thissection is shunted and its contacts thereafter remain in their releasedpositions with the result that energy is not supplied to the winding ofrelay AIIFSA and the contacts of this relay become released, therebyinterrupting both the circuit of the winding of relay AI IBSA and of thesnubbing resistor 4| so that the contacts of the relay AIIBSA becomereleased. v 5 I I 1 On release of contact 48 of relay AI IBSA thecircuit of the Winding 49 of the interlocking relay XR. is interrupted,and the armature controlled by this winding becomes released andinitiates operation of the crossing signals XS.

It will be seen that on shunting of the track relay AI I TR the contactsof this relay move to their released positions, if they are not alreadyin that position. On movement of the track relay contacts to theirreleased positions the supply of energy to the winding of the relay AlIFSA is cut off, while contact 36 establishes the circuit to supplyenergy to the rails of section BI IT. This energy feeds to the trackrelay BI ITR. and picks up the contacts of the track relay with theresult that there is a change in energization of the primary winding ofthe decoding transformer BI IDT and an impulse of energy is supplied tothe winding of the relay BI IH. The operation of the equipment is such,therefore, that on shunting of the track relay AI ITR an impulse ofenergy is supplied to the winding of the relay BI IH subsequent to theinterruption of energy to the Wind'- ing of the relay AI I FSA.

As a result of this supply of energy to the winding of the relay BI I H,the contacts of the relay are maintained picked up, and contact 5|maintains the circuit for supplying energy to the winding 53 of theinterlocking relay XR. The relay BI IH is of a type the contacts ofwhich are slow in releasing and this relay is selected so that itscontacts wi1 l remain picked up until after the contacts of the relayAIIBSA become released.

The contacts of relay AI IBSA release very soon after the contacts ofthe relay AI IFSA release as the circuit of the snubbing resistor 4| isinterrupted on release of the contacts of relay AI IFSA. and release ofthe contacts of the relay BI IH need not be delayed long after therelease of the contacts of relay AI IFSA to insure that the circuit ofthe winding 53 of the interlocking relay XR will not be interrupteduntil after the contact 48 of relay AI IBSA becomes released tointerrupt the circuit of the winding 49 of the interlocking relay )3.

Since the winding 49 of the relay XR is deenergized before the winding53 is deenergized, the armature controlled by the Winding 49 releasesfirst and subsequent release of the armature controlled by the winding53 will not interfere with the control of the crossing signals.

On release of the contacts of the relay AI IBSA the circuit whichincludes a back contact of the track relay for supplying energy to therails of section BI IT is interrupted, and the circuit for supplyingcoded energy of reverse relative polarity to the rails of section BI ITis established. Accordingly coded current of reverse relative polarityis supplied to the rails of section BI I T and the auxiliary track relayBI ITRA responds to this energy, while the contacts of the track relayBl I TR remain released.

As the contacts of relay BIITR remain re leased, energy is no longersupplied through the decoding transformer 13! IDT to the winding of therelay Bl IE and the contacts of relay Bl iH become released to conditionthe signal HS to display its red or stop indication, and to change theenergy supplied to the section in the rear from 180 to 75 codefrequency. In addition, contact i interrupts the circuit of the winding53 of, the interlocking relay XR, and the armature controlled by thiswinding moves toward its released position. However, as the armaturecontrolled by the winding 49 is already in the released position, thearmature controlled by winding 53 is prevented from moving all of theway to its released position. i

As a result of code following operation of the auxiliary track relay BilTRA, energy is supplied to the windings of the relays BHFSA and BHBSAand contact 56 of relay BHBSA be"- comes picked up to establish acircuit to supply energy to the winding 53 of the interlocking relay XR.Accordingly the armature controlled by the winding 53 becomes picked up,while the armature controlled by winding 49 remains in its releasedposition and maintains the crossing sign'als active.

From the foregoing it will be seen that when a train traveling in thereverse direction of traffic enters section A! iT, the supply of energyto the winding $9 of the interlocking relay XR. is cut off and that thisrelay initiates operation of the crossing signals. In addition at thistime the supply of energy of normal polarity to the section Bi ITR. iscut off so that energy is no longer supplied to: the winding of therelay Bl 11-1, but

that the contacts of. the relay Bl lH remain picked up long enough tomaintain the supply of energy to the winding 53 of the interlockingrelay XR, until after the winding i9 is cleenergized so that operationof the crossing signals is controlled by the armature which iscontrolled by the winding 49.

When the train advances far enough in the track stretch to enter sectionBUT, the relay Bl iTRA is shunted and ceases to follow code with theresult that the contacts of relays Bl IFSA and Bi iBSA become released.On release of contact of relay Bi iBSA the supply of energy to thewinding 53 of the interlocking relay XR is interrupted. The armaturecontrolled by this winding,

therefore, moves towards its released position, but

is prevented from moving all of the way to that position since the otherarmature of the relay is already in its released position.

7 When the rear of the train clears section l2T, the track relay of,this section responds to coded energy of the 180 code frequency, and thesignal E28 is conditioned to display its clear indication, while energyof the 180 code frequency is supplied to the rails of section Al IT.

When the rear of the train vacates section AH'I, coded energy feeds tothe track relay Al ITR and produces code following operation of therelay so that the windings of relays A! iFSA and AHBSA are energized. Onpicking up of the contacts of the relay AHBSA the circuit for supplyingcoded energy of reverse relative polarity to the rails of section BHT isinterrupted, while the circuit for supplying coded current of normalrelative polarity to section Bi ET is established.

In addition, on picking up of the contacts of the relay Ai iBSA contact48 establishes the circuit to supply ene'rggy to the winding 49 of theinterlocking relay XRL. Accordingly the armature controlled by thiswinding becomes picked up and discontinues operation of the crossingsignals XS, while because of the internal construction of the relay thearmature controlled by the other winding of the relay is prevented frommoving to its released position on picking up of the armature controlledby winding 49.

As long as any portion of the train remains in section Bi iT, the trackrelays for the section continue to be shunted, but when the rear of thetrain vacates the section, coded direct current of normal relativepolarity feeds to the track relay B! iTRand produces code followingoperation of th relay. As a result, energy is sup plied through thedecoding transformer Bl IDT to the windings of the relays Bi HI and BHJand the contacts of these relays become picked up to establish thecircuit of the green or clear lamp of signal HS. I

In addition, on picking up of the contacts of the relay Bi iI-I theenergy supplied to the rails of section GT is changed from '75 to codefrequency, while contact 5| establishes the circult to supply energy tothe winding 53 of the interlocking relay XR and the armature controlledby this winding becomes picked up.

The system provided by this invention employs polarized direct currentin the track circuits, and the current employed in adjoining trackcircuits may be of opposite relative polarity to prevent improperoperation of the signaling system in the event theinsulated jointsseparating two sections are defective so that energy from one tracksection feeds across the defective joint to the rails of the adjoiningsection. With this arrangement energy feeding feeding from the rails ofone section across a defective joint to the rails of the adjoiningsection will be of the polarity opposite to that which is employed inthe section to which the energy feeds, and since the code followingtrack relays will respond to energy of one polarity only, they will notrespond to energy supplied from the adjoining track circuits since it isof the Wrong polarity.

Where the rails of a track section are normally supplied with codedenergy of one relative polarity for the purpose of controlling thesignals governing traffic in the stretch, and at other times aresupplied with coded energy of the other relative polarity for detection.purposes, as is the case in the approach section Bl IT, it is necessaryto provide means energized from the rails of the section and responsiveto cur-- rent of both polarities;

Accordingly, if energy from section l'fiT feeds across defective jointsto the rails of section Bi 5T, the track circuit apparatus of section BlIT will respond to this current.

The equipment associated with section BHT may be arranged so that eitherone of the two track relays will not respond to energy of the polaritysupplied from the rails of section HIT, but the preferred arrangement isthat in which the track relay Bi lTR does not respond to this energy.If, therefore, the insulated joints separating the sections MT and BHTare defective so that coded energy from section iiiT feeds to the railsof section BUT, the track relay Bl l'IR will not respond to this energyand the signal US will not be improperly conditioned to display aproceed indication at times when section Bi PI is occupied.

The energy which feeds over defective joints fiorr'i section EST to therails or section BHT will effect operation of the track relay BI I'I'RAso that the windings of the relays BI IFSA and BIIBSA are energized andcontact 56 of relay B! IBSA is picked up and establishes the circuit inthe normal direction the track relays BI ITR and BI I TRA are shuntedwhen the train enters section BI IT, and operation of the crossingsignals XS is initiated as explained above. The energy from section IIiTfeeding across the defective joints is not effective to operate thetrack relay Bi I'I'RA until the rear of the train is located somedistance in advance of the entrance end of the sec-tion. Accordingly thecrossing signals will be operated for a period prior to the time atwhich the train reaches the highway intersection, and users of thehighway will have an indication of the approach of the train.

' Since coded current of both relative polarities is supplied to therails of section BI IT, if the joints separating the rails of thissection from section AI IT become defective, energy of one or the otherpolarity supplied to the rails of section BI IT will effect operation ofthe track relay AI ITR.

In the preferred embodiment the equipment is arranged so that the trackrelay Al I TR Will respond to energy of the polarity employed in thetrack section B! IT for detection purposes. When energy of this polarityis supplied to the rails of section BIIT, the section AIIT is occupiedso that energy supplied at the exit end of section AIIT does not feed tothe track relay AIITR. If energy of reverse relative polarity feeds overdefective joints to the relay AIITR, the relay will respond to the codedenergy until the contacts of relay AI IBSA become picked up. Thisinterrupts the supply of energy to section BI IT until the contacts ofrelay AtIBSA become released, whereupon the cycle is repeated. As aresult, energy of the code frequency is intermittently supplied to therails of section BIIT and there is no possibility that the signal liswill be improperly conditioned to display a proceed indication.

From the foregoing it will be seen that this invention provides animproved railway signaling system in which coded direct current of onerelative polarity is employed in a track circuit to control the trafficgoverning signals, while coded direct current of the other relativepolarity is employed in the track circuit at times for detectionpurposes.

While the invention has been illustrated and described in connectionwith the control of a highway crossing signal, it should be understoodthat the invention is not limited to use in this connection and that itmay be employed wherever it is desired to ascertain occupancy of a tracksection.

Although I have herein shown and described only one form of railwaysignaling system embodying my invention, it is understood that variouschanges and modifications may be made therein within the scope of theappended claims without departing from the spirit and scope of myinvention.

Having thus described my invention, what I claim is:

1..In a coded railway signaling system, in combination, a stretch ofrailway track having a pair of track rails divided by insulated jointsinto successive track sections, one of said sections including anintersection with a highway, the rails of said section having insulatedjoints therein adjacent the intersection to divide the section into aforward and a rearward subsection, means governed by traffic conditionsin advance of the section for selectively supplying to the rails of theforward subsection energy coded at either of a plurality of differentfrequencies, a code following electroresponsive device receiving energyfrom the rails of the forward subsection, means responsive to codefollowing operation of said device for supplying to the rails of therearward subsection direct current of one relative polarity coded at thesame frequency as the energy supplied to said device, means controlledby said device and operative when said device is not responding to codedenergy to supply to the rails of the rearward subsection coded directcurrent of the other relative polarity, a first and a second codefollowing electroresponsive device receiving energy from the rails ofthe rearward subsection, the first device being responsive to directcurrent of said one relative polarity only and controlling meansgoverning the supply of coded current to the rails of the adjacentsection in the rear of the rearward subsection, the second device beingresponsive to the supply of direct current of the other relativepolarity, a crossing signal protecting said highway intersection, meansresponsive to code following operation of said first device formaintaining said crossing signal inactive, and means responsive to codefollowing operation of said second device for also maintaining saidcrossing signal inactive.

2. In a coded railway signaling system, in combination, a stretch ofrailway track having a pair of track rails divided by insulated jointsinto successive track sections, one of said sections including anintersection with a highway, the rails of said section having insulatedjoints therein adjacent the intersection to divide the section into aforward and a rearward subsection, means governed by trafiic conditionsin advance of the section for selectively supplying to the rails of theforward subsection energy coded at either of a plurality of differentfrequencies, a code following electroresponsive device receiving energyfrom the rails of the forward subsection, means responsive to codefollowing operation of said device for supplying to the rails of therearward subsection direct current of one relative polarity coded at thesame frequency as the energy supplied to said device, means controlledby said device and operative when said device is not responding tocodedenergy to supply to the rails of the rearward subsection coded directcurrent of the other relative polarity, a first and a second codefollowing electroresponsive device receiving energy from the rails ofthe rearward subsection, the first device being responsive to directcurrent of said one relative polarity only and controlling meansgoverning the supply of coded current to the rails of the adjacentsection in the rear of the rearward subsection, the second device beingresponsive to the supply of direct current of the other relativepolarity only, a crossing signal protecting said highway intersection,means responsive to code following operation of said first device formaintaining said crossing signal. inactive, and means responsive to codefollowing operation of said second device for also maintaining saidcrossing signal inactive.

3. .In a coded railway signaling system, in combination, a stretch ofrailway track having a pair of a plurality of different frequencies, acode following electroresponsive device receiving energy from the railsof the forward subsection, means responsive to code following operationof said device for supplying to the rails of the rearward subsectiondirect current of one relative polarity coded at the same frequency asthe energy supplied to said device, means controlled by said device andoperative when said device is not responding to coded energy to supplyto the rails of the rearward subsection coded direct current of theother relative polarity, a. crossing signal protecting saidintersection, and means receiving energy from the rails of said rearwardsubsection, said means being operative when and only when responding tocoded direct current of either relative polarity to maintain thecrossing signal inactive, said means being operative when not respondingto coded energy of said one relative polarity to establish a firstsupply circuit for supplying energy of one code frequency to the railsof the section in the rear of said rearward subsection and beingoperative when and only when responding to coded direct current of saidone relative polarity to interrupt said first supply circuit and toestablish a second supply circuit for supplying to the rails of thesection in the rear of the rearward subsection energy of. a second codefrequency.

4. In a coded railway signaling system, in combination, a stretch ofrailway track havinga pair of track ra ls divided by insulated jointsinto successive track sections, one of said sections including anintersection with a highway, the rails of said one section havinginsulated joints therein adjacent the intersection to divide the sectioninto a forward and a rearward subsection, means governed by trafficconditions in advance of the section for selectively supplying to therails of the forward subsection energy coded at either of a plurality ofdifferent code frequencies, a code following track relay for the forwardsubsection having a winding receiving energy from the rails of saidforward subsection, a first supply circuit through which direct currentof one relative polarity may be supplied to the rails of the rearwardsubsection, a second supply circuit through which alternating currentmay be supplied to the rails of the rearward subsection, said first andsecond supply circuits each including a contact of said track relaywhereby when said track relay is responding to coded energy each of saidsupply circuits is interrupted at rates such that the energy suppliedthrough said supply circuits is coded at the same frequency as theenergy supplied to said track relay, a third supply circuit throughwhich direct current of the other relative polarity may be supplied tothe rails of the rearward subsection, means for periodicallyinterrupting said third supply circuit, means responsive to andoperative when and only when rails of said rearward subsection, saidmeans being operative when and only when supplied with coded directcurrent of either relative polarity to maintain said crossing signalinactive, said means being operative when not sup-plied with vcodedenergy of said one relative polarity to establish a circuit to supplyenergy of a first code frequency to th rails of the adjacent section inthe rear of said rearward subsection and being operative only on thesupply of coded direct current of said one relative polarity to cut offthe supply of energy of the first code frequency and to establish acircuit to supply coded energy of a second code frequency to the railsof th adjacent section in the rear of said rearward subsection.

5. In a coded railway signaling system, in combination, a stretch ofrailway track having a pair of track rails divided by insulated jointsinto successive track sections, one of said sections including anintersectionwith a highway, the rails of said one section havinginsulated joints therein adjacent the intersection to divide the sectioninto a forward and a rearward subsection, means governed by trafficconditions in advance of the section for selectively supplying to therails of the forward subsection energy coded at either of a plurality-ofdiiferent code frequencies, a code following track relay for the forwardsubsection having a winding receiving energy from the rails of saidsubsection, an auxiliary relay associated with said track relay, meansresponsive to code following operation of said track relay for supplyingenergy to the winding of said auxiliary relay, said auxiliary relaybeing operative when energized to establish a first supply circuitthrough which direct current of one relative polarity may be supplied tothe rails of the rearward subsection and being operative when notenergized to establish a second supply circuit through which directcurrent of the other relative polarity may be supplied to the rails ofthe rearward subsection, the first supply circuit including a contact ofthe track relay whereby energy supplied through said circuit is coded atthe same frequency as the energy supplied to said track relay, means forintermittently interrupting the second supply circuit to code thecurrent supplied through said circuit, a crossing signal protecting saidintersection, means receiving energy from the rails of the rearwardsubsection and operative on the supply of coded direct current of eitherrelative polarity to maintain said crossing signal inactive, said meansbeing operative when not supplied with coded energy of said one relativepolarity to establish a circuit to supply energy of a first codefrequency to the rails of the adjacent section in the rear of saidrearward subsection and being operative when and only when coded directcurrent of said one relative polarity is supplied thereto to cut off thesupply of energy of the bination, a stretch of railway track having apair of track rails divided by insulated joints into successive tracksections, one of said sections including an intersection with a highway,the rails of said one section having insulated joints therein adjacentthe intersection to divide the section into a forward and a rearwardsubsection, means governed by traflic conditions in advance of thesection for selectively supplying to the rails of the forward subsectionenergy coded at either of a plurality of different code frequencies, acode following track relay for the forward subsection having a windingreceiving energy from the rails of said subsection, an auxiliary relayassociated with said track relay, means responsive to code followingoperation of said track relay for supplying energy to the winding ofsaid auxiliary relay, said auxiliary relay being operative whenenergized to establish a first supply circuit through which directcurrent of one relative polarity may be supplied to the rails of therearward subsection and to also establish a first shunt circuit by meansof which connection may be established between the rails of the rearwardsubsection, each of said circuitsincluding a contact of the track relayand being arranged so that one circuit is established in one position ofthe track relay contact and the other circuit is established in theother position of the track relay contact, said auxiliary relay beingoperative when deenergized to establish a second supply circuit throughwhich direct current of the other relative polarity may be supplied toth rails of the rearward subsection and to also establish a second shuntcircuit by means of which connection may be established between therails of the rearward subsection, means for alternately interruptingsaid second supply circuit and said second shunt circuit at apredetermined rate, sad means being operative to interrupt each of saidcircuits before establishing the other of said circuits, a crossingsignal protecting said intersection, and means receiving energy from therails of the rearward subsection and operative on the supply of codeddirect current of either relative polarity to maintain the crossingsignal inactive, said means being operative when not supplied with codeddirect current of said one relative polarity to establish a circuit tosupply coded energy of a first code frequency to the rails of theadjacent section in the rear of said rearward subsection and beingoperative when and only when supplied with coded direct current of saidone relative polarity to cut off the supply of energy of the first codefrequency and to establish a circuit to supply energy of a second codefrequency to the rails of the adjacent section in the rear of saidrearward subsection.

'7. In a coded railway signaling system, in combination, a stretch ofrailway track having a pair of track rails divided by insulated jointsinto successive track sections, one of said sections including anintersection with a highway, the rails of said one section havinginsulated joints therein adjacent the intersection to divide the sectioninto a forward and a rearward subsection, means governed by traiiicconditions in advance of the section for selectively supplying to therails of the forward subsection energy coded at either of a plurality ofdifferent code frequencies, a code following track relay for the forwardsubsection having a winding receiving energy from the rails of saidsubsection, an auxiliary relay associated with said track relay, meansresponsive to code following operation of said track relay for supplyingenergy to the winding of said auxiliary relay, said auxiliary relaybeing operative when and only when energized to establish a first supplycircuit through which direct cur-- rent of one relative polarity may besupplied to the rails of the rearward subsection and being operativewhen and only when deenergized to establish a second supply circuitthrough which direct current of the other relative polarity may besupplied to the rails of the rearward subsection, each of said supplycircuits having associated therewith means for periodically interruptingsaid circuit to thereby supply coded energy to the rails of the rearwardsubsection through said supply circuit, a crossing signal protectingsaid intersection, and means receiving energy from the rails of therearward subsection and operative on the supply of coded direct currentof either relative polarity to maintain the crossing signal inactive,said means being operative when not supplied with coded direct currentof said one relative polarity toestablish a circuit to supply codedenergy of a first code frequency to the rails of the adjacent section inthe rear of said rearward subsection and being operative when and onlywhen supplied with coded direct current of said one relative polarity tocut off the supply of energy of the first code frequency and toestablish a circuit to supply energy of a second code frequency to therails of the adjacent section in the rear of said rearward subsection.

8. In a coded railway signaling system, in combination, a stretch ofrailway track having a pair of track rails divided by insulated jointsinto successive track sections, one of said sections including anintersection with a highway, the rails of said one section havinginsulated joints therein adjacent the intersection to divide the sectioninto a forward and. a rearward subsection, means governed by traflicconditions in advance of the section for selectively supplying to therails of the forward subsection energy coded at either of a plurality ofdifferent code frequencies, a code following track relay for the forwardsubsection having a winding receiving energy from the rails of saidsubsection, an auxiliary relay associated with said track relay, meansresponsive to code following operation of said track relay for supplyingenergy to the winding of said auxiliary relay, said auxiliary relaybeing operative when and only when energized to establish a first supplycircuit through which direct current of one relative polarity may besupplied to the rails of the rearward subsection and being operativewhen and only when deenergized to establish a second supply circuitthrough which direct current of the other relative polarity may besupplied to the rails of the rearward subsection, each of said supplycircuits having associated therewith means for periodioally interruptingsaid circuit to thereby supply coded energy to the rails of the rearwardsubsection through said supply circuit, the rearward subsection having afirst and a second code following track relay each having a windingreceiving energy from the rails of said section, said first track relaybeing responsive only to direct current of said one polarity, saidsecond track relay being responsive to direct current of the otherpolarity, a crossing signal protecting said highway intersection, meansresponsive to code following operation of either of said track relaysfor maintaining said crossing signal inactive, and means responsive tocode following operation of said first track relay for controlling thesupply o-f coded energy to the rails of the adjoining section in therear of said rearward subsection, said means being operative when saidfirst track relay is not responding to coded energy to establish acircuit to supply energy of a first code frequency and being operativewhen said first track relay is responding to coded energy to establish acircuit supply energy of a second code frequency to the rails of saidadjoining section in the rear of said rearward subsection.

9. In combination, a stretch of railway track intersected by a highwayand comprising a signal approach section and a signal clearing section,a crossing signal for the intersection, means efiective when saidclearing section is unoccupied for supplying to the rails of theapproach section train governing code comprising impulses ofunidirectional current of one relative polarity, means responsive toentrance of a train into said clearing section for interrupting thesupply of train governing code to the rails of said approach section andfor supplying thereto detection code comprising impulses ofunidirectional current of the other relative polarity, a first and asecond electroresponsive device associated with said approach section,each of said devices having a winding receiving energy over the rails ofthe said approach section, the first device being responsive only to thesupply of current of said one relative polarity and the second devicebeing responsive to the supply of current of the other relativepolarity, whereby said first device responds only to the train governingcode and the second device responds to the detection code, and meansresponsive to code following operation of either of said devices formaintaining said crossing signal inactive, whereby said signal isinactive when the approach and clearing sections are unoccupied and isrendered active on entrance of a train into the approach section and isagain rendered inactive when the train advances into the clearingsection and vacates the approach section.

10. In combination, a stretch of railway track intersected by a highwayand comprising a signal approach section and a signal clearing section,a crossing signal for the intersection, means effective when saidclearing section is unoccupied to supply to the rails of the approachsection train governing code comprising impulses of unidirectionalcurrent of one relative polarity, means responsive to entrance of atrain into said clearing section for interrupting the supply of traingoverning code to the rails of said approach section and for supplyingthereto detection code comprising impulses of unidirectional current ofthe other relative polarity, and electroresponsive means receivingenergy from the rails of said approach section and responsive to thesupply of coded energy of either relative polarity to maintain the crosssignal inactive, whereby said signal is inactive when the approach andclearing sections are unoccupied and is rendered active on entrance of atrain into the approach section and is again rendered inactive when thetrain advance into the clearing section and vacates the approachsection.

11. In a coded railway signaling system, in combination, a stretch ofrailway track having a pair of track rails divided by insulated jointsinto successive track sections including adjoining forward and rearwardsections, the forward section including an intersection with a highwayand being divided into an approach and a clearing subsection, a crossingsignal for said intersection, means effective when the clearingsubsection is unoccupied to supply to the rails of the approachsubsection train governing code comprising impulses of unidirectionalcurrent of one relative polarity, means responsive to entrance of atrain into said clearing subsection for interrupting the supply of traingoverning code to the rails of said approach subsection and forsupplying thereto detection code comprising impulses of unidirectionalcurrent of the other relative polarity, and electroresponsive meansreceiving energy from the rails of said approach section, said meansbeing operative on the supply thereto of either train governing ordetection code to maintain the crossing signal inactive, said means alsobeing operative when not supplied with train governing code to efiectthe supply of train governing code of a first character to the rails ofsaid rearward section and being operative when supplied with traingoverning code to efiect the supply of train governing code of a secondcharacter to the rails of said rearward section, whereby said crossingsignal is inactive and train governing code of the second character issupplied to the rails of said rearward section when said approach andclearing subsections are unoccupied, and on entrance of a train into theapproach subsection the signal is rendered active and train governingcode of the first character is supplied to the rails of said rearwardsection, andwhereby the signal is again rendered inactive when the trainadvances into the clearing subsection and vacates the approachsubsection while train governing code of the first character is suppliedto the rails of the rearward section until the train vacates theclearing subsection and thereafter train governing code of the secondcharacter is supplied to the rails of said rearward section.

GEORGE W. BAUGHMAN.

